Improving the cellular uptake of oligonucleotide analogues represents a critical issue with respect to the application of these biomolecules in the targeting of mRNAs or in the formation of triplex structures with genomic DNA as a means to control gene expression. Studies related to improve cellular uptake of oligonucleotide analogues have been scarce and poorly executed as far as refinement of the parameters is concerned. Our approach involves the systematic tailing of an oligonucleoside phosphorothioate of known biological activity against HIV, with monomeric polyethylene glycols at either the 3'-end, 5'-end or both ends and assay for the untailed phosphorothioate oligomer in chronically infected H9 cells. So far we have synthesized four different oligonucleoside phosphorothioates complementary to the mRNA encoded by the rev gene of HIV each of them covalently bound at both ends to 1, 2, 3, or 4 hexaethylene glycol monomer(s). These oligonucleotides have been purified to homogeneity on denaturing polyacrylamide gels and are ready for biological evaluation. All of these oligonucleotide analogues formed stable DNA duplexes with their complementary DNA sequences relative to the untailed oligonucleoside phosphorothioates. (The duplexes have the same Tm at 260 nm). It is to be noted, however, that the hexaethylene glycol monomers were linked together by phosphodiester bridges. To properly study the effect of added charges on the behavior of these biomolecules, oligonucleoside phosphorothioates will also be derivatized at the 3'-end with uncharged polyethylene glycol molecules of varying sizes (M.W. 1,000-8,000). Judith b. Regan has already purified a phosphorothioate oligomer conjugated to a relatively large polyethylene glycol monomer (M.W. 2,500). Tm experiments are currently being conducted., Dr. Mitsuya of the NCI will perform all the biological assays pertaining to these novel biomolecules.